Chemical sensors are used to detect the presence of a metal cation in a substance and are useful in a variety of fields. Typically, a colorimetric reagent is immobilized on a support, such as optical fibers, and the sensor is applied in biomedical uses, process control, and environmental analysis. Detection of calcium ions (Ca(II)) is useful, for example, in detecting the amount of calcium in the blood of animals, or in detecting calcium in the food processing industry. The colorimetric reagent reacts with the calcium ion in a substance or solution so that there is a change in an optical property; for example, absorption, luminescence, or reflectance, and correlated with the concentration of the calcium ion. This is accomplished by correlating the concentration of the calcium ion to a calibration curve which relates the optical property to the concentration of the calcium.
Sensors which have been developed to this point have several deficiencies, including a slow response time because of barriers to mass transport at the polymer support, a low sensitivity due to weak analytical signal, a low selectivity due to interferences, and a long term instability because of degradation of the immobilized reagent or its desorptive loss from the support.
This invention relates to an improved sensor which provides for a rapid response time and high sensitivity through the use of a porous polymer film as the support material for the analytical reagent. High selectivity, and resistance to degradation are achieved by employing a calcium ion sensitive colorimetric reagent having sulfonic acid or carboxylic acid binding to the anion exchange polymer and calcium ion chelating groups.
A primary object of the invention is to provide for an improved chemical sensor of calcium ions in a solution or substance.
It is an objective of this invention to provide a chemical sensor for calcium ions which has a rapid response time.
A further object of the invention is to provide for a highly sensitive chemical sensor of calcium ions.
Yet a further object of the invention is to provide a chemical sensor with high selectivity for calcium ions.
Another object of the invention is to provide a chemical sensor which is resistant to degradation.
A still further object of the invention is to provide a chemical sensor in which the analytical reagent has strong binding to the underlying polymeric support.
Further objects of the invention will become apparent in the following disclosure.